1. Field of the Invention
The present invention relates to managing methods and managing apparatuses used in monitors, and in particular to methods and apparatuses for adjusting the luminosity of a monitor based on an image.
2. Description of the Prior Art
Generally, in an LCD monitor with a back light source, the luminosity of the light source is kept as a constant. The amount of light that passes through the liquid crystal molecules in the monitor is controlled by adjusting the rotation angles of the liquid crystal molecules. In this way, the brightness of the images displayed on the monitor can be changed. On the other hand, an image is composed of plural pixels having various gray levels (i.e. brightness). The rotation angle of one liquid crystal molecule is decided according to the gray level of the pixel corresponding to that liquid crystal molecule. In a monitor capable of displaying 256 gray levels, for example, gray level 255 corresponds to the highest brightness, and gray level 0 corresponds to the lowest brightness. Please refer to FIG. 1, which illustrates an example of the relationship between gray levels and brightness. As shown in this example, gray levels are directly proportional to the brightness of LCD monitors substantially.
In actual conditions, not every image includes pixels having gray level 255. In some images, the brightest pixel might only have gray level 200, or even lower. In prior arts, even the gray level of the brightest pixel in a displayed image is 200, the luminosity of the light source in the LCD monitor is still kept at the level capable of displaying gray level 255. Under this kind of condition, the luminosity of the light source is not adequately utilized. That is, lots of light is sheltered by rotated liquid crystal molecules. Therefore, when a darker image is displayed, the utility rate of the light source of an LCD monitor may be only 80%; the other 20% luminosity is not well utilized.
As known by those skilled in this art, the back light source of an LCD monitor consumes much power, for instance, 70%˜80% power consumption among that of the LCD monitor. The higher luminosity a back light source has, the more power is consumed by the LCD monitor. Furthermore, when an LCD monitor is operated, the light source therein is always turned on. Obviously, this low utility problem of back light sources induces much unnecessary and undesired power consumption